Process of tanning leather and product thus produced



United States Patent F PROCESS OF TANNING LEATHER AND PRODUCT THUS PRODUCED Frank A. Edmonds, Arlington Heights, and Russell P. Doyle, Chicago, 111., assignors to American Cyanamid Company, New York, N .Y., a corporation of Maine No Drawing. Filed Sept. 6, 1957, Ser. No. 682,323

2 Claims. (Cl. 8-94.33)

This invention relates to a process for taming hides and to the product thus produced. Still further, this invention relates to a process for retanning tanned hides and to the product thus produced. More particularly, this invention relates to a process for tanning leather comprising treating untanned or tannned hides with (1) dicyandiamide, (2) a water dispersible melamine-formaldehyde resin and (3) a lignosulfonate, in an aqueous medium, until said hides are tanned.

One of the objects of the present invention is to tan untanned hides or to retan tanned hides in order to get leather skins which are fuller and tighter and which have improved cutting value and improved flexible dyeability.

A further object of the present invention is to treat leather with an aqueous dispersion of dicyandiamide, a water dispersible melamine-formaldehyde resin and a lignosulfonate until the leather is retanned. These and other objects of the present invention will be discussed in greater detail hereinbelow.

In the conventional preparation of untanned hides for tanning, after the hair is removed and the hides are properly delimed and hated, the hides are thoroughly wetted in an acidic liquor, very frequently at a pH between about 15 and 6 and at room temperature until the hidm are thoroughly pickled. This preparatory step may be carried out over a wide range of temperatures such as between about 40F. and 120 F. but preferably between 85 and 100 F. If for a particular reason relating to the desired end properties in the ultimate product, one wishes to adjust the pH of the wetting out liquor to control the hand of the ultimate product, one may adjust the pH, for instance, to about 4 or 5 just prior to the practice of the present invention. Such adjustment of the pH can be accomplished by the addition of a suitable acidic material or an alkaline material depending on Whether or not it is desired to raise the pH from 3 to about 4-5 or whether or not it is desired to lower the pH from about 6 to about 4-5. More frequently than not, one will desire to raise the pH by using such materials such as sodium acetate, borax, sodium bicarbonate, sodium formate, calcium formate or any suitable alkaline material. Strongly alkaline materials should either be avoided or used with the necessary caution.

The process of the present invention is equally applicable to tanned hides as well as to untanned hides. The tanned hides to be treated in the process of the present invention may be hides which have been tanned by a vegetable extract or blends of extracts of which many are known in the art or in a metal tanning process such as chrome tanning and the like of which many are well known in the art. All that has been said hereinabove with respect to the conventional procedure for treating untanned hides is equally applicable to the treatment of tanned hides. It is, in fact, preferred to utilize the process of the present invention in its application to tanned leather in a retanning operation.

a In the practice of the process of the present invention,

2,970,033 Patented Jan. 31, 1961 ice one may treat the tanned or untanned hides with an aqueous dispersion of (l) dicyandiamide, (2) a water dispersible melamine-formaldehyde resin and (3) a lignosulfonate in an aqueous medium until said hides are tanned. Alternatively, one may treat the hides with an aqueous dispersion of dicyandiamide and water dispersible melamine-formaldehyde and then add to the treating medium a lignosulfonate or one may treat the hides with an aqueous dispersion of dicyandiamide and a lignosulfonate and then add a water dispersible melamine-formaldehyde resin to the treating bath. Each of these alternatives produces desirable results.

The dicyandiamide used in the practice of the process of the present invention will be present in the treating liquor in amounts varying between about 0.5% and 10% by weight based on the total weight of the hides to be treated. Preferably, one would use between about 1.5 and 2% by weight of dicyandiamide based on the total weight of hides to be treated. In the place of part or all of the dicyandiamide, one could use guanyl urea, guanidine, byguanide and other comparable materials or mixtures of two or more of these materials may be used in the place of part or all of the dicyandiamide.

The melamine-formaldehyde resins used in the practice of the process of the present invention may be prepared by reacting melamine and formaldehyde in mol ratios varying between about 1:1 and 1:6 but preferably between about 1:2 and 1:3, melamine to formaldehyde, respectively. These melamine-formaldehyde condensation products may be completely water soluble or they may merely be water dispersible of which many are known in the art. The water soluble class of resin may be one in which the reaction between the melamine and the formaldehyde has not gone significantly past the methylol stage and is considered to be practically monomeric and devoid of any significant condensation. Being water soluble at this point, they are obviously water dispersible. The alkylated melamine-formaldehyde resins may be used as well, provided that they are water dispersible including water soluble. These alkylated melamine-formaldehyde resins are prepared by reacting a lower aliphatic monohydric alcohol such as methanol or ethanol with a methylol melamine such as the monomethylol melamine, dimethylol melamine, trimethylol melamine, tetnamethylol melamine, pentamethylol melamine and hexamethylo1 melamine. The amount of lower aliphatic alcohol used to react with the methylol melamine on a mol basis will depend in great measure upon the degree of methylolation in the resin and, as a consequence, may be varied between about 1:1 and 1:6 melamine to alcohol, respectively. Methanol is the preferred monohydric alcohol to be used in making alkylated melamine-formaldehyde resin and the product produced is a methylated melamineformaldehyde resin. The methylated melamine-formaldehyde resin is preferred over the unalkylated melamineformaldehyde resin which latter, of course, is simply the reaction product of melamine and formaldehyde alone as essential reactants. Reference is made to the US. Patent 2,715,619 for one of the processes which may be used for the preparation of the resins used in the practice of the process of the present invention. The amount of melamine-formaldehyde resin, alkylated or unalkylated, which is used in the practice of the process of the present invention on a resin solids basis may be varied between about 0.5 and 10% by weight based on the total weight of the hides to be treated. Preferably, one would use between about 2% and 5% by weight, same basis. Other aminotriazine aldehyde condensation products may also be used provided that in the stage in which they are used, they meet the description of water dispersibility. Included are the form-aldehyde reaction products of such 1 materials such as formoguanamine, acetoguanamine, N,

salts of lignosul fonic acid. Many ofthese lignosulfonates are commercially available such as the sodium, calcium and ammonium lignosulfonates. Since these lignosulfonates in their commercial availability are frequently sold as mixed lignosulfonates, it isobvious that mixtures of lignosulfonates may readily be used. The amount of lignosulfonate used in the practice of the process of the present invention may be varied between about 0.5% and 20% and preferably 05-10% by weight based on the total weight of hides to be treated. Preferably, one would use between 3% and 8% by weight, same basis.

The process of the present invention is particularly applicable to metal tanned leathers such as chrome tanned leathers, zirconium tanned leathers, aluminum tanned leathers and the like. Leathers tanned with vegetable extracts may also be treated by the process of the present invention. Whether tanned or untanned, the starting materials of the present invention. are thoroughly wetted with water, generally at a pH between about 2 and 6 and preferably between 4 and 5,- at temperatures between 40 F. and 120 F. and preferably between 85 and 100 F.

In carrying out the process of the present invention, the temperature of the liquor in which the hides are steeped may be maintained between about 60 and 160 F. and preferably between 90 and 140 F. The time of treatment will vary between 30 minutes and 24 hours and will depend on the temperature of thetreating bath and will also depend on whether it is a tanning or retanning process. The time may be varied between about 30 minutes and 2 hours when employed as a retanning process. Longer periods of time may be used but no significant additional take-up is accomplished and the added time simply increases the cost of the operation and for this reason may well be avoided. When employed as a tanning process, 6 to 24 hours will be required. The volume of water used in the treating bath may be' varied between about 10% and 400% and even more, based on the total weight of the stock to be treated. Preferably, onewould use between about 50% and 100% by Weight of water based on the total weight of the stock.

Any of the conventional equipment used in the tanning of leather may be used in the practice of the process of the present invention including the closed rotating drum in which the aqueous dispersion of the materials contained the wetted out stock are rotated so as to tumble the hides thoroughly in the treating liquor. Additionally, one could make use of a paddle vat which apparatus and its use is well known in the art.

Either of the alternative methods set forth hereinabove is to be practiced; one may, for instance, introduce the dicyandiamide and the water dispersible melamine-formaldehyde into the aqueous medium and treatment of the stock may be carnied out for a brief period of time such as about 5 to minutes and then the lignosulfonate may be added and the treatment continued until the hides are tanned. On the other hand, one could introduce the (licyandiamide and the lignosulfonate into the treating medium, carrying out the treatment of the hides for brief periods of time, as above, and then add the water dispersible melamine-formaldehyde resin. Regardless of the alternative chosen, the lignosulfonate or the melamine-formaldehyde resin should be-added to the treating medium containing the dicyandiamide at a time prior to the completion of the treating process. If the treating process is to be carried out for a full two-hour period or longer in a retanning process, the-third component should he added to the system not later than about one and a half hours after the commencement of the process.

One of the outstanding features of the present inven tion resides in the fact that the stock being treated may be dyed with considerable control. If desired, the coloring material in the nature ofa dye and/or a pigment may be introduced into the treating medium at the beginning of the operation or at any stage in the course of the process or the treated stock may be dyed after the process has been completed. Where it is desired to dye the stock thoroughly and completely, the dyestuff should be introduced at the beginning of the process. On the other hand, if it is desired only to impart coloration to the surface or upper layers of the stock being treated, the dye may be introduced into the treating medium at the halfway point or even beyond. Any of the conventional dyes or pigments may be used in the practice of the process of the present invention.

The pH of the treating medium may be varied considerably on the acidic side depending of the type of leather desired. If one desires a soft type of leather, the pH may be controlled at about 5-6. If firm leather is desired, the pH may be controlled at about 4-5. If harder types of leather are desired, the pH may be controlled at about 3-4. For most practical purposes, at the completion of the treating steps, the leather most desired from a property standpoint is one in which the pH has been adjusted at the completion of the process to about.4-4.2. Thereafter, the conventional steps for the treatmentof tanned leathers are observed. For instance, the treated'hides are then rinsed, washed in preparation for the application of oils, as is conventional. The washing temperature is generally controlled sons to be within the range of the temperature of oil application such as at about ll'0l50 F. The oils are generally added to lubricate the hides. This oil treatment imparts a considerable measure of suppleness to the treated hides. Additionally, one can treat the oil treated tanned leather with fillers such as wheat flour, colloidal clay and the like, while the hides are still in a wet state. Thereafter, the hides are dried or stretched and then dried. If one so desired, one could use additionally,,in the practice of the process of the present invention, any of the other tanning materials in addition to those required in the present invention such 'as the naphthalene or phenol base syntans and the like.

In order that the practice of the process of the present invention may be more completely understood, the following examples are set forth in which all parts are parts by weight unless otherwise indicated. These examples are set forth primarily for the purpose of illustration and any specific enumeration of detail contained therein should not be interpreted as a limitation on the case except as is indicated in the appended claims.

Example 1 Pieces of chrome tanned cowhide previously split to the desired thickness, weighing 210 parts are thoroughly wet back with water at F. Thereupon an addition of a 33 /3% basic commercially available chrome tanning salt is added, in the proportion of 2%, based upon the above weight, and the leather is drummed for one hour to obtain the desired eifect. At this stage sufficient alkali is added to raise the basicity of the chrome tanning salt in order that the'desired combination of said chrome salt with the hide protein might be eifeoted.

After washingout the excess uncombined materials present in the stock, the pH of the samples is raised to 5 by the addition of alkali; Subsequent washing and draining isemployed to bring the leather to a condition desir-able for the application of the additional retanning materials.

Based upon the aforementioned weight, there is added of water at F. containing 5 of sodium lignosulfonate, 2% dicyandiamide, 0.75% acid dye and of a methylated ether of trimethylol melamine. The temperature of the treating bath is held at about 120 F. and the leather is tumbled in the solution for approximately 60 minutes. Thereafter, the pH of the system is adjusted to 4.3 by the addition of a sufiicient amount of an aqueous solution of formic acid. The tumbling is continued for an additional 15 minutes whereupon the leather is drained and washed for 5 minutes at 120 F. and drained. Thereafter, the leather is treated with conventional amounts of sulfonated and raw oil in the form of an emulsion and milling is continued for some 30 minutes. The leather is then dried in a conventional manner and is ready for subsequent finishing processes.

Example 2 Example 1 is repeated in detail except that the leather is not tanned with a chrome tanning salt prior to the application of the lignosulfonate, dicyandiamide and the methyl ether of the methylol melamine.

Comparisons made between the resultant leathers from Examples 1 and 2, and leathers retanned with vegetable extracts plus lignosulfonate plus acid naphthalene syntan, plus dye, indicated improved color value from the dyestufl, improved tightness and break, comparable thickness and increased area in the leather retanned according to Examples 1 and 2 beyond that obtained from the conven tional vegetable extract method of retanning. In addition to these aforementioned advantages, there was no drawn grain in the leather from Examples 1 and 2, whereas, there was evidence of this condition in the conventional vegetable retanned leather.

Example 3 Pieces of chrome tanned cowhide previously split to the desired thickness, weighing 250 parts are thoroughly wet back and retanned with a suitable commercial basic chrome tanning salt as in the manner described in Example l.

The leather is then washed and drained and 100% water at 100 F. is then added. 1% of a neutral naphthalene syntan is then added and milled for 15 minutes. The pH of the system is then raised by additions of sodium acetate to 4.95. The solution is then drained and the leather is washed for minutes at 120 F. and drained. There is then added 110% water at 120 F., 5% of a methylated trimethylol melamine, 2% dicyandiamide, 4% sodium lignosulfonate and 0.75% of an acid dyestuff (Calcocid Fast Red A). The total charge is milled for about 90 minutes at the stated temperature of the water. Thereupon, 0.5% formic acid is added and milled for 10 minutes. The pH is 4.0. The aqueous solution is drained and the treated leather washed for 5 minutes at 125 F. and drained.

To the wet leather there is added 50% water at 125 F. An emulsion of 7% sulfonated sperm-neats foot oil combination, of a medium degree of sulfonation, 1% raw neats-foot oil and 25% water is added at 125 F., followed by milling for 20 minutes, whereupon an emulsion of 3% of highly sulfonated neats foot oil in 10% water is added at 125 F. and 10 minutes additional milling is provided.

The leather is piled overnight, wrung to remove excess water, set and dried by hanging at room temperature.

The resultant leather was very full, round and tight. There was no significant grain draw and a considerable increase over the original thickness. The dye had penetrated to about one-half the thickness of the leather and did not crock to any extent on both wet and dry rubbing.

Example 4 100 parts by weight of chrome retan calfskin leather is thoroughly soaked in water at a pH of 3.9, is washed with water and then soaked in 100 parts of water at 100 F. 1 part of a neutral naphthalene syntan is added with 10 parts of additional water and it is milled for minutes whereupon part of sodium acetate is added, milled for 10 minutes whereupon an additional half part of sodium acetate is added and milled for 20 minutes. The pH of the solution is 4.95. The aqueous solution is drained. The hides are washed for 10 minutes in 120 F. water and then drained. There is then added parts of water at F., 5 parts of a methylated trimethylol melamine resin, 2 parts of dicyandiamide, 4 parts of sodium lignosulfonate and .75 part of a dye (Calcocid Fast Red A) and the total charge is milled for about 90 minutes at the stated temperature of the water. Thereupon, part of formic acid is added and milled for an additional 10 minutes. The pH is 4.0. The aqueous solu tion is drained; the treated leather washed for 5 minutes at F. and drained. To the wet leather, there is added 50 parts of water at 125 F. An emulsion of 7 parts of sulfonated sperm and neats foot of medium sulfonated oil, 1 part of raw neats-foot oil and 25 parts of water is added at 125 F. followed by milling for 20 minutes thereupon an emulsion of 3 parts of a highly sulfonated neats-foot oil in 10 parts of water is added at 125 F. followed by milling for 10 minutes. The hides are piled overnight, wrung and set and then hung to dry. The resultant leather was very full and round with no significant draw. There was a considerable increase in thickness over the original weight. The dye had penetrated to about /2 the thickness of the leather and did not crock to any extent on both wet and dry rub.

soaked in an acid liquor, adjusted to a pH of 4.6. The

hide is removed, washed and drained The hide is then introduced into 50 parts of Water at 120 F. containing 5 parts of methylatedtrirnethylol melamine, 2 parts of dicyandiamide, 0.1 part of fast light orange dye and the charge is milled for 30 minutes. The pH of the solution is 4.5. An additional 50 parts of water at 120 F. is added containing 10 parts of a commercial liquid sodium and calcium lignosulfonate preparation. The milling is continued then for 30 minutes. The pH of the solution is 4.7. The leather is then removed, washed and drained and treated with the oil as is conventional.

Example 6 Example 5 is repeated in all details except that the liquid lignosulfonate is added with the dicyandiamide in the absence of the methylated trimethylol melamine and the methylated trimethylol melamine is added in the subsequent part of the process where the lignosulfonate had been added in the preceding example. The pH of the solution after the dicyandiamide and lignosulfonate had been added was 4.55 and remained constant after the addition of the resin. The leathers treated according to Examples 5 and 6 each showed very good break, the leather from Example 6 being slightly better. The leather from Example 6 was definitely softer than the leather for Example 5. Each of the leathers was substantially the same with respect to fullness and the leather of Example 5 was firmer.

Example 7 Twelve sides Weighing 100 parts of chrome tanned cowhide leather, split at 44% ounces that had been thoroughly wetted and neutralized to a pH of 4.5 were drained, washed and drained and then introduced into 80 parts of water containing 1.75 parts of dicyandiamide, 5 parts of lignosulfonate and .125 part of acid orange dye. The material is milled for 20 minutes, the pH is 4.5-4.6 and the penetration is complete. There is then added 10 parts of water and 5 parts of methylated trimethylol melamine. Milling is continued for 30 minutes. The pH remains constant and the solution is clear. 0.25 part of formic acid in 10 parts of water are added and the milling is continued for 15 minutes. The pH is 4.0 and the solution is clear. An equal quantity of formic acid and water is again added and the material is milled for 15 more minutes. The leather is drained, washed for minutes at 130 F. and drained again. The conventional oil and filler treatment is given and the hides horsedovernight and subsequently set out and dried.- The leath er produced was full and round and showed good wet" break.

Example 8 Example 7 is repeated in substantially all essential details except that the amount of resin used was 4 parts of methylated trimethylol melamine instead of 5 parts. The resultant leather had a good break, a smooth surface and the fullness and roundness and color were good. No grain draw was observed.

Example 9 18 sides of chrome tanned cowhide, split at 3 /2 to 4 ounces, and weighing 150 parts, had been thoroughly wet back, washed at 120 F. for minutes and drained. 80% water at 120 F. is then added and 0.5% sodiurr'i acetate is added and subsequently milled for minutes to raise the pH value to 4.3. 5% sodium-calcium lignosulfonate, plus 2% dicyandiamide plus 0.125% acid dyestuii in 30% water is then added and drummed for 30 minutes. The aqueous solution is then drained off the leather and the leather is washed for 5 r'ninut'es at 130 F. The drum is again drained and then there is added 80% water at 130 F. and 3% tfim'ethylol melamine. The leather is milled in this solution for 45 minutes. The aqueous solution is drained 01f the leather and the leather is rinsed for 3 minutes at 130 F. and subse-. quently drained. p

30% water at 130 F. and 1.5% of a commercial filler is added and milled for' 15 minutes. A suitable emulsion of raw oils containing a cationic type e'niulsifier is added and drummed into the leather. The spent liquor is drained and an emulsion ofan anionic sulfonated sperm oil is added and milled for a further minutes. U

The leather is then piled overnight, set out and dried, at which point it is ready to receive the conventional finishing operations.

Example 10 Pieces of full weight pickled kipskin, weighing 500' parts, are thoroughly wet back by drumming in 100% water, containing 7% common salt at a temperature of 75 F. for 15 minutes. The solution pI-lis 3.1 at this time.

Then there is added 20% of a commercial calcium base, liquid lignosulfonate, containing 50% solids, and

8 2% dicyandiamide. Milling is continued for 3 hours and the solution pH is 3.85.

At this time 20% more water, 5% methylated trimethylol melamine and 2% anhydrous sodium acetate is added and milling is continued for several hours more. The skin is allowed to remain in contact with the tannirig liquor overnight. On the following morning 2 hours further milling is given.

At this time the excess tanning materials are removed by Washing for 10 minutes at F. and the water is drained from the leather.

The leather is lubricated with a sulfonated-raw neat foot oil emulsion at F. for 45 minutes and is then allowed to stand overnight before drying.

Full, round, plump leather in a light tan shade is 01 tained. A uniform cross sectional color was observed, with no raw or untanned section in the interior. No drawn grain was noticed.

The process of the present invention is applicable to hides which are conventionally used in the production of leather and to the tanned leathers produced therefrom. Illustrativeof these hides are cow hides, horse hide, calfskin, kidskin, sheepskin, goatskin, liZar'd skin, alligator skin, ostrich skin, pigskin and the like.

We claim:

1. A process for tanning leather comprising soaking hides in an aqueous tanning liquor containing between about 0.5% and 10% by weight of dicyan'diamide, betweenabout 0.5% and 10% by weight of a water-dispersible methylated melamine-formaldehyde resin and between about 0.5% and 20% by weight of a lig'nosulfonate at a temperature between about 60 F. and F. and at a pH between about 3' and 6 until said hides are tanned, said percentages being based on the weight of said hides.

2. A process for retanning leather comprising soaking tanned hides in an aqueous tanning liquor containing between about 0.5% and 10% by weight of dicyandiamide, between about 0.5% and 10% by weight of a water-dispersible methylated melamine-formaldehyde resin and between about 0.5 and 20% by weight of a lignosulfonate at a temperature between about 60 F. and 160 F. and at a pH between about 3 and 6 until said hides are retanned, said percentages being based on the weight of said hides.

References Cited in the file'of this patent UNITED STATES PATENTS Marvel Feb; 17, 1948 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION f Patent No, 2,970,033 January 31, 1961 Frank A. Edmonds et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 57, for "for" read from column 7, line 25, for "30%- read 20% column 8, line 42, for "60 F.:" read 60 F.

Signed and sealed this 25th day of July 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer 1 Commissioner of Patents 

1. A PROCESS FOR TANNING LEATHER COMPRISING SOAKING HIDES IN AN AQUEOUS TANNING LIQUOR CONTAINING BETWEEN ABOUT 0.5% AND 10% BY WEIGHT OF DICYANDIAMIDE, BE TWEEN ABOUT 0.5% AND 10% BY WEIGHT OF A WATER-DISPERSIBLE METHYLATED MELAMINE-FORMALDEHYDE RESIN AND BETWEEN ABOUT 0.5% AND 20% BY WEIGHT OF A LIGNOSULFONATE AT A TEMPERATURE BETWEEN ABOUT 60*F. AND 160* F. AND AT A PH BETWEEN ABOUT 3 AND 6 UNTIL SAID HIDES ARE TANNED, SAID PERCENTAGES BEING BASED ON THE WEIGHT OF SAID HIDES. 